Porosity and Microstructure of Underwater Wet FCAW of Duplex Stainless Steel

Abstract

Flux-cored arc welding (FCAW) of duplex stainless steels has been widely used in offshore engineering, nuclear power engineering, and petroleum pipe lines. But underwater wet welding repair technology is still impossible for avoiding pore defects in welds. To study how pores perform in underwater wet welds, underwater wet flux-cored arc welding of S32101 duplex stainless steel was carried out in a hyperbaric chamber. The evolution of porosity and microstructure with welding parameters in 20 and 60 m water depth was analyzed for comparison. The relationship between porosity and austenite morphology in microstructures was discussed. Decreased welding parameters can increase the cooling rate. As a result, the ferrite to austenite transformation can be promoted and the resultant microstructures can be refined. Lower welding speed prolongs the high-temperature retention time, which is helpful to gas escaping from the molten pool. As a result, the porosity of the welds decreases. Reduced welding voltage with finer microstructure prevents the porosity in both water depths. It was found that the coarser the austenite microstructure was, the higher the porosity was. Additionally, the welds conducted with bigger welding current in 20 m water depth have lower porosity, the same as the welding speed, while the situation is reversed in 60 m water depth for a coarser austenite microstructure.